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  • #16
    Basic question for you all. Does HP/torque increase directly with air volume (assuming the same final compresion ratio) or is there some other advantage to turbo/super charging? In other words, other than engine weight what's the difference between a turbo engine and a proportionaly larger engine with a combustion chamber small enough to provide the same compresion ratio?

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    • #17
      HP out is pretty linear with air/fuel mass, modulo power to drive compressor. An intercooled turbo can generate more power
      than a bigger engine w/ a higher compression
      ratio since the latter will detonate due
      to a higher charge temperature. Also, a larger engine cannot spin as fast as a small one, so small engines built stout w/ lots of intercooled boost will make a lot of power
      given the right fuels (alcohol).

      <font face="Verdana, Arial" size="2">Originally posted by Dave Opincarne:
      Does HP/torque increase directly with air volume (assuming the same final compresion ratio) or is there some other advantage to turbo/super charging? In other words, other than engine weight what's the difference between a turbo engine and a proportionaly larger engine with a combustion chamber small enough to provide the same compresion ratio?</font>
      Bart Smaalders
      http://smaalders.net/barts

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      • #18
        Some guy runs around town with a sharp little turbo hanging off the side of his HOG. No2 system if you think he is kidding and a front break that looks like it might work. go figure. Try looking for some HOG hot rodder.

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        • #19
          RE:............ In other words, other than engine weight what's the difference between a turbo engine and a proportionaly larger engine with a combustion chamber small enough to provide the same compresion ratio?

          Tons of difference. First off, you DON'T want your turbo engines C.R. to equal a normally asperated one. You want it to be lower. Reason; more space = more air/fuel mixture that the turbo can cram in to it and that equals more HP. Usually it is skewed towards the top end. An engine that has a lower CR will have a longer throttle response time though.

          From about 1980 to 1989 or so F1 allowed 1500cc(91.5 CID) turbocharged engines to compete directly w/3000cc NA ones. Within a few years you either had a turbocharged engine or were relagated to the back of the pack. The best 3000cc (181CID) NA engines made (then) around 650-675 HP. The turbos made from 700 to 1000 hp depending on the boost (later actually adjustable from the the cockpit). Towards the end of that formula teams actually had turbocharged engines built strictly for qualifying. That is one lap warm up two or three laps at ABSOLUTE MAXIMUM speed and one lap cool down (actually just hope it hung together long enough to get it back to pits!). Those engines made between 1100 to 1250 HP and were ONLY designed to last five or six laps MAX.

          In the late 60's - early 70's Porsche built a flat 18 cylinder motor (490 CID) as an engineeing excercise and to be used if their twin turbocharged, flat 12 cylinder (5.4 L) motor did not put out enough power. That motor(5.4L) made 1200 HP from 326 CID and could do so for short periods of time. It was usaully rated at 750 HP to 850 HP and could win Le Mans (24 hrs flat out) in that state of tune. When Porsche got out of Cam Am racing in 1973, after winning the series for two years in row they retired the 18 cyl car too. It made just over 2000 HP but was never needed.

          One of the best books on state of the art turbocharged engines is "Anatomy of the F1 Racing Cars" from, I believe, Classic Motorbooks, in Osceola, Wisconsin. You need to find the one that came out in the late 80's or early 90's. I'm not sure that it is still in print though.

          Neat trick about the brushless DC motor RR. I liked it!

          Regards, Ken

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          • #20
            Sorry Steve. I wasn't dissing you. It's hard to determine technical attainments and the questions behind the questions from a posting or two particulalry if the starting info is sparce.

            I'd suggest to anyone posting a technical question that a sentence or two discussing respectively their background, the present stituation, what they want to happen, the resources available, and the budget if germain.

            If I presented too much too and basic info is its possible it will benefit someone if not the original poster.

            As for your lack of info from company and distruibutor sources, I couldn't say. If your original info came from a magazine it's very possible the lower levels have little knowledge of what new products may be happening in their company's future. Then too magazines frequently garble little details and report tentative discussions and rumors as established fact. Magazines have pages to fill to attract readers and thus accrue advertizing revenue.

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            • #21
              forrest,
              i didnt mean to be abrasive, i was a little cranky when i wrote that, i had just got up. and yes, it is good for someone to read to benefit. any info is good info.
              no hard ones,

              steve
              extreme tractor racing

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              • #22
                Thanks for your response Ken, but thats a little two much detail for me, give it to me simpley. In the example you give, is the 1500 cc turbo breathing more or less air than the 3000 cc engine? As I understand it, for any given fuel displacement isn't realy what counts, but how much air/fuel gets crammed into the combustion chamber.

                Interesting about the outcome of the turbo/NA outcome. I remember watching some F1 races when both types where running and recall that the NA engines had a real advantage everywhere but the straight aways since they didn't suffer a lag time. They would realy hit the brakes hard if a turbo was behind them and then take advantage of the quicker low end tourqe.

                TIA - Dave

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                • #23
                  Hi Dave,

                  Re:...........is 1500 cc turbo breathing more or less air than the 3000 cc engine?

                  WAY MORE AIR!!! The name of the game is getting as much air as you can into and out of a motor. Out is usually NO PROBLEM. The pistons will always push it out and the induction/exhaust piping can be used to "tune" the engine to use the weight of the air/fuel charge to actually pull out the spent gasses. This is done along with cams, head porting size and angle and length of headers and intake manifolds. Now it can all come together at only one single RPM range. You set up your motor for top end in dragsters and some kind of comprimise RPM for road racing. It depends on the tracks longest straight, number and type of corners and your transmission and final gear ratios. You always want the car to be accelarating. You want the engines to top out at the end of the longest straight (idealy)!
                  You can always get enough fuel into an engine but air movement and control is the name of the game.
                  After the turboes got thier act together for endurance and turbo lag they came off the corners like they were shot out of a cannon. Since they weighed less they also accelerated harder too! When they were allowed unlimited fuel thier higher HP made them untouchable. Figure 1000 HP in a 1800# car.

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                  • #24
                    Wa-a-ay back when I was a budding motor head I was interested in F-1 when it was 1500 cc NA only. There was a cartoon in one of the mags showing "trombone" tuning of the induction stacks and the exhaust complete with flyball governor Rube Goldberg operating mechanism. Hilarious. I had it in my tool box for years and got laughs all the ding dong time (never clean and reorganize your tool box.

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                    • #25
                      call

                      TURBOCHARGERS INC (901) 366-1646
                      3867 OLD GETWELL RD
                      MEMPHIS, TN 38118


                      they should be able to obtain it or cross it with a garrett for you. randy t

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                      • #26
                        Ok, so torque has a more or less linier relation with air volume and the advantage of a turbo is how weight affects engine dynamics? SDDWGOSA(standard disclaimers dealing with gross oversimplifications apply)

                        Ken-I don't understand how a turbo can have a lower effective CI if more air is being drawn in.

                        -Dave (4" stroke, likes a tiny primary, 5k redline and 4.11 gears so I don't use a turbo but could use a good tri-Y header)

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                        • #27
                          dave O, i think you and ken are talking about two different things, static compression ratio versus cylinder pressure.
                          my feeling is cylinder pressure = torque. i know you like to use the word linear dave, but i dont feel that any engine is linear. they are usually kind of S curve. some i guess could be more linear than others, but usually once the valves start floating your horsepower goes bye bye. haha. a motor is a pump, agreed? a given motor will have a given volumetric effiency. the engine in the car you drive has a v.e. of about 75% (generic) with improvements in cylinder head, cam timing events and other modifications, it is possible to exceed 100% V.E. most prostock engines,nascar engines are over 100. heres where a turbo charger excels above naturally aspirated. V.e. is drastically improved because in effect " you are pumping air into the pump(motor)" if that is the simplest way to explain it to an engineer, i dont know what is. also, its not just high volume , but also pressurized. 8 psi of boost run in an engine with 9-1 static compression ratio produces a given amount of cylinder pressure, which equates to torque. horsepower scales upwards with boost pressure. the more boost you run, the more hp you will make. the limiting factor now is detonation in the motor, you ever see those pulling tractors with three stage turbos on them? they are running gobs of boost. they use water injection to cool the intake charge and quench detonation. amazingly they are almost using more water than fuel in a pull. thats why when you see one of those old allisons pulling, everyone gets back, with all that boost, when those 12's let go, parts go a flyin! there are many other aspects of the turbo, and i am no expert, i figured i would share some generic info for everyone.
                          extreme tractor racing

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                          • #28
                            OK, I got it compresion ratio doesn't take into account how well the engine breaths (partial vacum at the bottom of the stroke?) and the turbo effectivly improves intake efficiency to greater than 100% as compared to a larger NA engine Yes?

                            I know power curves aren't linier, I'm just trying to grossly oversimplify in order to get at the nub of my question.

                            Thanks All.

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                            • #29
                              and the light goes on, bling
                              extreme tractor racing

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                              • #30
                                I recall a honda motorcycle using a tiny turbo, less than 1" diameter, I think. I wondered at the time if it wasn't possible to gate the inlet to the turbo, and drive it with a brushless motor, using an ironless armature. The limitation on speed would depend on the bearings then, and if attached to the turbo shaft, that's solved, also. Electronics would have no trouble keeping up, even at 250 krpm. I mention the gate firstly since it would allow the turbo to come to speed, and remain there, essentially in a vacuum, before any flow was req'd of it. Secondly, I brought it up because no one else did. Is it just a bad idea?
                                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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